1. Field of the Invention
The present invention relates generally to a data transmitting device and method for a wireless communications system, and in particular, to a device and method for retransmitting data that has errors during transmission.
2. Description of the Related Art
For forward packet data transmission, a mobile station is assigned a forward channel such as a dedicated channel (DCH) from a base station. Wireless communications systems as mentioned below include satellite systems, ISDN, digital cellular systems, W-CDMA, UMTS, and IMT-2000. Upon receipt of the forward packet data, the mobile station determines whether the reception is successful and if it is, the mobile station transmits the packet data to its higher layer. On the other hand, if errors are detected from the packet data, the mobile station requests its retransmission by the HARQ (Hybrid Automatic Repeat Request) scheme. HARQ is a retransmission scheme using both FEC (Forward Error Correction) and ARQ (Automatic Repeat Request) for requesting retransmission of a data packet having errors. HARQ increases transmission throughput and improves system performance by channel coding for error correction. The main channel coding methods are convolutional coding and turbo coding.
A HARQ system uses soft combining to increase throughput. There are two types of soft combining: packet diversity combining and packet code combining. These are also referred to as soft packet combining. Despite having lower performance characteristics relative to packet code combining, packet diversity combining is widely used when performance loss is low, due to its simple implementation.
In general, it is known that there is little performance difference between packet diversity combining and packet code combining for convolutional codes with a low code rate. However, the difference is conspicuous for turbo codes because iterative decoding and parallel recursive convolutional codes are used. For the turbo codes, packet code combining offers a greater performance gain than packet diversity combining.
In this case, it is difficult to transmit multiple data. “Multiple data” is defined as data with different characteristics or service qualities in one packet. Wireless communications systems do not transmit multiple data. Therefore, the existing methods have limitations in carrying out transmission and retransmission of multiple data. Moreover, existing systems cannot increase transmission throughput when multiple data is retransmitted by ARQ.